1. Field of the Invention
The present invention relates to a deaerating apparatus for deaerating a resist solution which is applied to a substrate of a liquid crystal display device (LCD) or the like; a deaerating method; and a treatment apparatus using the deaerating apparatus.
2. Description of the Related Art
Generally, in fabricating an LCD substrate, a circuit pattern is formed by photolithography technique; a resist solution is applied to the LCD substrate and exposed to light beams in correspondence to the circuit pattern; and then the circuit pattern is developed.
In the resist-applying and developing treatments, a developing solution and a resist solvent such as thinner are used in addition to the resist solution. These treatment solutions contain gas for various reasons. The gas causes the following disadvantages.
For example, if the resist solution containing gas is applied to the substrate, it foams thereon. Consequently, the substrate is covered with the resist solution nonuniformly. Similarly, if the developing solution containing gas is applied to the substrate, it foams thereon. Consequently, the substrate is partly undeveloped. If a solvent such as thinner contains gas, pores are formed on a resist film.
To solve such problems, the following deaerating methods are proposed:
As a known liquid-deaerating method (first example), using a vacuum pump, a liquid accommodated in a pressure-reduced tank is deaerated under vacuum.
According to the method (second method) of deaerating a developing solution disclosed in Laid-Open Japanese Patent Application No. 9-7936, a liquid flowing in a tube made of fluororesin is vacuum-aerated in the outside of the tube to remove only gas from the liquid through pin holes thereof.
The method of the first example is capable of deaerating the inner part of the liquid to a comparatively high degree, whereas it deaerates its inner part insufficiently. That is, the method has a poor deaerating performance.
In the method of the second example, because it is impossible to reduce the thickness of the tube not to make the degree of its strength low, the tube has a low degree of gas permeability. Thus, the method has an insufficient deaerating performance. In addition, the method necessitates the installation of equipments of a large scale because it is necessary to supply a large amount of treatment solution to the process of applying the resist solution to LCD substrates and developing the circuit pattern.